Also VERY important is making sure diameters and
lengths not only MATCH yourengine's needs but also howyour vehicle is equipped, itsintended use PLUS yourown expectations as well!(See
Header Questionnaireto find out what needs tobe considered.)

(Note that no mention of
Brand Name nor Cost was
mentioned in the above
list of Performance Header
Design Parameters as
engines do not respond
to product names nor
product costs - they ONLY
respond to good design!)

Keep in mind that, as the tube
size increases, exhaust gas
velocity INSIDE the tube at
any given RPM decreases.
For example: Looking at the
above chart, choosing a 2"
tube rather than 1 7/8" lowers
the gas velocity in the header
tube about 14.6%; Choosing
a 2"
tube rather than 1 3/4"lowers the gas velocity in the
header
tube about 32.6%.

It has been our experience
(by listening to fellows
complain about headers
they've bought elsewhere)
that
if one misses the correct
header tube
size by two tube
sizes
LARGER than needed
(one
commits the infamous
"TWO TUBE SIZE ERROR"),
the gas
velocities inside
the header tubes can be
25-50% (or more!)
slower
than
they should be. These
much lower gas velocities
effectively take away
the headers' ability to
scavenge exhaust gases
optimally - resulting in
reduced bottom end and
mid-range performance and
sometimes even reduced
top end power as well!
Anyone
who believes that
BIGGER IS
BETTER has
obviously
NEVER
experienced this header
design error!

==================

One comparison missing
in the above chart is the
area difference between
2 1/2" and 3" OD tubing.
3" is 46% larger in area
than 2 1/2". This means
that, in a 3" exhaust
system, the gas velocity
is about 46% SLOWERthan it
would be in a
2 1/2"
system.

While the above Tube
Area Differences chart
compares inside areas
of various
header and
collector tube
sizes,
maintaining high gas
velocities in the exhaust
system is also important.
(Think of the exhaust
system as a secondary
scavenging system located
immediately behind the
headers!). This is why
many switching to or
using 3" exhaust systems
often complain about
the poor bottom end and
mid-range performance of
their engines - the inside
area difference between
these two tube sizes can
end up simply too big
and the resultant much
lower gas velocities
inside
these 3" systems
actually ends uphurting performance
in many situations!

==================

(Tube Inside Area
calculations assume .049"
wall thickness on 3" OD
and
smaller tubing and
.060" wall thickness on
3 1/4" and larger tubing.)(The above Tube Area
Differences chart is a
smaller version of a much
larger chart found in ourHeader Design InfoPak.)

==================

RPM Range Definitions

Throughout this website
discussion often references
various engine rpm ranges.
Considering engines capable
of producing PEAK HP around
6000 rpm, we would define
the rpm ranges as follows:

"Bottom End", "Low End"
- off-idle to 3000 rpm

"Mid-range"
- 3000 to 4500 rpm

"Top End", "High End"
- 4500 and higher rpm

(These rpm ranges are
approximate and would also
vary proportionately as peak
HP rpms go up or down.)

Referencing to actual use:

"Bottom End" covers rpms
of stock or near stock stall
convertors, rpms in town
driving or cruising down
highways, etc.;

All of our tubing bends are mandrel bent (wrinkle-free) to insure a consistent inside diameter throughout the bend. Unless mentioned otherwise, all bends are made from 18 gauge material. Except for the three Stainless Steel J-Bends listed immediately above, ALL of our bends are made from Mild Steel. We offer NO bends made from Aluminum Tubing. All of our Mild Steel bends have 180 degree bends. We do NOT offer bends with other degrees of bend like 90 degrees, 45 degrees, etc. As fabricators we have learned that offering more choices of radii and leg lengths is FAR more important than offering different angle bends. The cost of building headers is also reduced when 180 degree bends are used throughout the construction process.

All tube sizes are O.D. (OUTSIDE DIAMETER).

The Radius of a bend is the centerline radius as measured from the center of the tubing to the actual center of the bend itself. Another way of looking at this is that the diameter of a bend (NOT the diameter of the tubing the bend is made out of) is double the radius of the bend so that if you measured ACROSS the bend from the center of one bend leg to the center of the other bend leg that measurement would be twice the radius of the bend.

For example: A 2" OD x 3" Radius U-Bend would measure 6" across the bend from the center of one leg to the center of the other leg. Dividing that measurement by 2 gives you the bend radius - 3" in this case.

If you need the measurement of a bend on the INSIDE from leg to leg, take the bend radius and double it to find the bend diameter and then SUBTRACT the bend TUBE diameter from that amount.

For example: A 2" OD x 3" Radius U-Bend would have a bend diameter of 6". SUBTRACTING the tube diameter of 2" would give you 4" - the INSIDE measurement of the bend from the inside of one bend leg to the inside of the other bend leg.

If you need the measurement of a bend on the OUTSIDE from leg to leg, take the bend radius and double it to find the bend diameter and then ADD the bend TUBE diameter from that amount.

For example: A 2" OD x 3" Radius U-Bend would have a bend diameter of 6". ADDING the tube diameter of 2" would give you 8" - the OUTSIDE measurement of the bend from the outside of one bend leg to the outside of the other bend leg.